Unloader for sleeve valve gas compressors



April 29, 1952 c. B. SMITH 2,594,315

UNLOADER FOR SLEEVE VALVE GAS COMPRESSORS Filed May 31, 1946 Y sSheets-Sheet 1 i g .96 9 3 .;z 5 J7 7 L32"; Q j l 51 g $0 1&4

.30 2%25 .30 26 J9 a9 44/ a 2 //VV/V7'O2 CZUSTOPHEK B. SMITH ATTORNEYSApril 29, 1952 c. B. SMITH UNLOADER FOR SLEEVE VALVE GAS COMPRESSORS 3Sheets-Sheet 2 Filed May 31, 1946 i k w WHMHHHHHU \NN.

Hnnfluwll r W ATTOQ/VEYS April 29, 1952 c. B. SMITH 2,594,315

UNLOADER FOR SLEEVE VALVE GAS CQMPRESSORS Filed May 31, 1946 5Sheets-Sheet s 4 TTOQNEYS Patented Apr. 29, 1952 UNLOADER FOR SLEEVEVALVE GAS COMPRESSORS Christopher Broom Smith, Naphill, England, as-

signor to Broom and Wade Limited, High Wycombe, England, a Britishcompany Application May 31, 1946, Serial No. 673,592

In Great Britain June 4, 1945 This invention relates to reciprocatorycompressors for air or gas of the type having a sleeve valve controllingthe admission of air to the cylinder from a suction chamber and itsdelivery to an intermediate delivery chamber from which 8 Claims. (Cl.23022) the air passes through a non-return valve to the outlet of thecompressor. It has been proposed to provide a compressor of this typewith a port in its cylinder head which communicates with the atmosphereand is controlled by a valve which normally closes the port but is opento place the cylinder in communication with the atmosphere and unloadthe compressor.

According to the present invention an air or gas compressor of the abovetype is provided with a passage extending from the intermediate deliverychamber (delivery to which is controlled by the sleeve valve) to theatmosphere or to the suction chamber and with an unloading valvearranged to open or close that passage.

The invention is particularly applicable to compressors in which one endof the sleeve valve reciprocates in an annular space between thecylinder and an inwardly-projecting part of the cylinder head. Theintermediate delivery chamber may be constituted by the portion of thisannular space beyond the end of the sleeve valve.

The invention will now be described, by way of example, as applied to areciprocatory compressor, and with reference to the accompanyingdrawings in which:

Figure l is a vertical section through a cylininder I l which issurrounded by a suction. chamberl2 communicating "with the cylinder byan annular port or series of ports l3. The'air inlet to the suctionchamber is indicated at Hi and.

water-jacket space around the cylinder at I5, 18.

'Within the cylinder there reciprccates a sleeve valve I1 and inside thesleeve valve a piston I8 operated by a connection rod 19, the. crank,crankcase and lower portion of the cylinder being omitted in the drawingas the construction of these parts is well understood. On the top of thecylinder there rests an intermediate head 2 plate '26 and above theinder head 2|, the head plate and the main head 2| together constitutingthe cylinder head and being secured by studs 22 and nuts 23. To theunderside of the intermediate head plate 20 there is secured aninwardly-projecting part 24 of the cylinder head, the part 24 beingsecured to the intermediate plate 20 by screws 25 and the whole of thethree parts of the head, 20, 2|, 24, being secured together by studs 23and nuts .21. The portion 24 of the cylinder head which pro jectsinwardly into the cylinder provides an annular space 28 between itselfand the inner wall of the cylinder ll whichfits the upper end of thesleeve valve I! and in which the upper end is able to reciprocate. Asuitable internal sealing ring 29 is provided in the top of the sleevevalve I! to afford the tight joint between it and the cylinder headportion 24. This portion 24 is formed with spaced passageways 30, formedby short flutes in its external surface at intervals around its loweredge, which passageways are always open to the cylinder but are coveredby the sleeve valve [1, which is raised during the suction stroke, sothat throughout this stroke the intermediate delivery chamber 28 is cutoil from communication with the cylinder.

During the delivery stroke the sleeve valve I! is lowered and uncoversthe communication of the passageways 30 with the intermediate deliverychamber 28 so'that the piston 18 may, during the delivery stroke, forcethe air through the passages into the intermediate delivery ber 28. v I

The intermediate head plate 23 is formed with an annular space 3|. inits under surface which constitutes a continuation of the intermediatedelivery chamber 28 and this space communicates through a ring of ports32 with the upper face of the intermediate head plate 23 where it lieswithin a large outlet port 33 formed within the main head casting 2!.the ring of ports 32 are closed byan'annular plate valve 34 which seatson the'upper surface of the intermediate head plate 23 above the ports32 and is urged downwardly by springs 35 held in recessesin aring-shaped casting 36 which overlies'but is spaced from the plate valve3 t.

The ring-shaped casting 36 is supported from the intermediate head plate20* by lugs 3'! which project from its underside and rest on the plate20,

these lugs being pierced by holes through which, pass fixing studs 38.

head plate 20 a main cyl-.

cham- The upper ends of The normal delivery. ofv the compressor thuspasses through the plate valve 34 into the outlet 33 and the annularde-- livery chamber 28 does not constitute any dead air space in thecompressor because after it has closed the communication of the spaceabove the piston IS with the intermediate delivery chamber through thepassages 33 at the end of the delivery stroke, the sleeve valve I?continues to move upwardly and forces air out of the intermediatedelivery chamber 28 through the valve 32 until the sleeve valve hasreached the top of the space afforded by the intermediate deliverychamber. When the valve H is near the top of its stroke it openscommunication between the suction chamber l2 and the interior of thecylinder owing to the ring of ports 39 in the sleeve valve coming intoregister with the inlet ports l3 in the cylinder wall.

The intermediate head plate 28 is also provided with a passage All whichleads out of the intermediate delivery chamber at 3! to one side of thecylinder to a position where it comes beneath an unloading port 4|formed in the main head casting 2|. The unloading port M is closed by aninverted lift-valve 62 which constitutes an unloading valve and isprovided with a stem extending upwardly through the cylinder head into acontrol cylinder 43. In the control cylinder 43 is a control piston 44which bears upon the stem of the unloading valve 52 and the piston andvalve tend to be lifted by a spring d5.

The control cylinder 53 is connected by a pipe 46 to an automatic pilotvalve, not shown in the drawing. The pilot valve is connected to the airreceiver to which the compressor delivers, or to some part connectedtherewith, and it admits pressure to the pipe 48 when the desiredworking pressure is reached. When air is admitted to the pip 46 itcauses the control piston to move down to open the valve 42 and placesthe passage in communication, through the port M, with a further portion41 of the passage which extends from the intermediate delivery chamberat 3!.

As can be seen from Figure 2 of the drawing, the passage 47 communicateswith a port 48 in the lower face of the head 21 and thence by way of aport 48 in the intermediate head plate. 29 and a passage 50 in thecylinder, which constitutes an extension of the passage M, with thesuction chamber l2.

In the operation of the unloading device, when the valve 42 is closedcompressed air is delivered to the outlet 33 through the plate valve 34.and builds up pressure, in the receiver or other vessel, to'which thecompressor delivers. When the air pressure has been built up to thepredetermined value, the pilot valve operates and delivers air underpressure to the pipe 43, thus causing the valve 42 to be opened. Whenthe valve is opened theair delivered by the piston to the intermediatedelivery chamber 28 passes from the intermediate delivery chamber by wayof the passage 40, port 41 and further extensions of the passages 4'!and 56, to the suction chamber I2. Return of air past the valve 42 isprevented because on the suction stroke of the compressor thecommunication between the intermediate delivery chamber 28 and thecylinder is cut off by the sleeve valve l1 and therefore all the airpassing into the cylinder enters it through the ports I3. After thesleeve valve I! has cut off the intermediate delivery chamber from thecylinder it continues to rise and delivers air through the unloadingport 4| to the suction chamber 52. In the suction belt l2 the relativelyhot air which has been expelled from the cylinder and to theintermediate delivery chamber becomes mixed 4 with atmospheric air fromthe inlet l4 and cooled before it is drawn again into the cylinder andredelivered through the unloading valve.

Two results follow from this arrangement of the unloading port, namely,first that as hot air is not sucked to and fro past the valve on bothsuction and delivery strokes of the piston, the valve is not subjectedto so much heating as in the case where the valve opens a directcommunication between the cylinder and the suction zone. The risk of thevalve reaching a high temperature and causing carbonization of the oilis therefore reduced. Secondly, as the intermediate delivery chamber 28is interposed between the cylinder and the unloading passages and thedirection of air flow is alway the same through these parts, and as alsoafter the piston has been shut off from the intermediate delivery.chamber the sleeve valve continues to deliver some air, there is lessnoise from the operation of the unloader than has previously been thecase.

Furthermore, as the valve 42 does not lie over the cylinder or directlycommunicate with it there is no risk of any damage being done should thehead of the valve break or the spring 45 break, while the compressor isin operation. With the prior construction it would have been possiblefor the valve head in these circumstances to fall into the compressorcylinder, or at least to come in contact with the head of the piston,and cause damage.

Referring to Figures 3 and 4, these, show a twocylinder compressorcomprising cylinders 60, 6|, which contain sleeve valves 62, 63 andpistons 64, 65. The cylinders are in a single block surrounded by awaterjacket space 63 and surmounted by an intermediate head plate 67 anda main head casting 63. There is a suction chamber 69 and air inlet it,the general arrangement of all these parts being similar to that alreadydescribed in connection with Figures 1 and 2. However, the constructiondifiersin that theunloading port H instead of being located in the headas in the case of the unloading port 4! of Figures 1 and 2 is located inthe cylinder block and the lift valve I2 which controls it has a stemwhich extends downwardly through a guide 13 into a chamber M at the sideof the cylinder block. The chamber 74 constitutes a passage whichconnects the unloading port with the suction chamber 69. The valve 12 isurged in a direction to close the port H by a spring (5.

As can be seen from the plan of Figure 4, there are two valves 72, one,for each cylinder, and the two valves are operated by a single lever 16having a forked end at 17, 78, the two arm of, the fork engaging thelower ends of the stems of the valves. The forked lever it is pivoted ona bracket i9 secured to the exterior of the'cylinder block and the leverpasses. to the outside of the cylinder block through a large aperture inthe side thereof. which aperture is covered by a casing 853. The casing89 embodies in it upper portion an actuating cylinder 3! which containsa piston H2 and is connected to an air-supply pipe 83, corresponding tothe pipe 16 of Figure l. Th space 84 in the intermediate head plate 6'1,which cor-" responds to the passage 40 of Figure l, is shaped so as toextend into the intermediate delivery chamber of each cylinder, asindicated by the chain lines 85 of Figure 4. It will be appreciated thatthe sectioned part of Figure 3 is taken upon an irregular plane which isapproxi-.

mately represented by the line 33 of Figure 4.

The operation is the same as in the case of Figures 1 and 2, in thisinstance both cylinders being unloaded simultaneously by operation ofthe same lever.

Although a piston and cylinder have been shown in the drawings foroperating the valves which control the unloading ports, it will beappreciated that a sore; or cam or other mechanical device could beemployed for operatin the valve either in addition to the piston oralternately thereto. The mechanical operation of the unloading devicemay be of service in cases where it is desired to start up thecompressor and connect it by hand to a system of pipe work which isalready under pressure, as where there are several compressors connectedto supply a single system.

I claim:

1. A compressor comprising, in combination, a cylinder, a sleeve valvereciprocable therein, a piston reciprocable within the sleeve valve,means for operating the sleeve valve and piston, a suction chamber inthe form of an annular zone around the cylinder communicating with thecylinder through ports controlled by the sleeve valve, an intermediatedelivery chamber communicating by ports controlled by the sleeve valvewith the cylinder, an outlet, a delivery valve between the intermediatedelivery chamber and the outlet, a passage extending from theintermediate delivery chamber into communication with atmosphere and anunloading valve arranged to open and close that passage.

2. A compressor as claimed in claim 1 wherein the passage extending fromthe intermediate delivery chamber, into communication with atmosphereleads into the suction chamber of the compressor which suction chamberis itself open to atmosphere.

3. A compressor as claimed in claim 1 wherein the cylinder has acylinder head with an inwardly-projecting portion aifording an annularspace between the cylinder and said inwardlyprojecting portion of thecylinder head, one end of the sleeve Valve reciprocates in said space,and the intermediate delivery chamber is constituted by a portion ofsaid annular space beyond the end of the sleeve valve.

4. A compressor as claimed in claim 1, wherein the unloading valve isconstituted by a lift valve opening against the flow of air from theintermediate delivery chamber to atmosphere and provided with means forlifting it from its seating against the pressure when unloading is tooccur.

5. A compressor as claimed in claim 1, wherein the unloading valve isconstituted by a lift valve opening against the flow of air from theintermediate delivery chamber to atmosphere, and wherein means areprovided for lifting the unloading valve from its seat comprising acylinder and piston and pipe connections for the supply of operatingpressure thereto.

6. A compressor as claimed in claim 1, wherein the cylinder comprisestwo cast parts, the one a main cylinder-body casting and the other acast cylinder head, with means to secure the head to the main casting,the unloading valve is a lift valve located in the cylinder head, andthe passage which is opened and closed thereby is constituted in part bya passage cast in the cylinder head and in part by a passage in the maincylinder-body casting, the two passage parts communicating by portsformed in the joint between the cylinder head and the main casting.

7. A compressor as claimed in claim 1, wherein the unloading valve is alift valve mounted on the cylinder of the compressor.

8. A. compressor, comprising, in combination, a cylinder' block and twocylinders side by side in the block; each cylinder having associatedtherewith a sleeve valve reciprocable therein, a piston reciprocablewithin the sleeve valve, means for operating the sleeve valve andpiston, a suction chamber in the form of an annular zone around thecylinder communicating with the cylinder through ports controlled by thesleeve valve, an intermediate delivery chamber communicating throughports controlled by the sleeve valve with the cylinder, an outlet, adelivery valve between the intermediate delivery chamber and the outlet,a passage extending from the intermediate delivery chamber intocommunication with atmosphere, and an unloading valve arranged to openand close that passage; and the two unloading valves are located side byside in the cylinder block and an operating lever engages both unloadingvalves and is operated by a single actuating means.

CHRISTOPHER BROOM SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,668,795 Aikman May 8, 19281,805,741 Prestage May 19, 1931 1,878,326 Ricardo Sept. 20, 19322,074,911 Hull Mar. 23, 1937 2,160,860 Gustafson June 6, 1939 2,231,904Gustafson Feb. 18, 1941 FOREIGN PATENTS Number Country Date 234,183Great Britain 1925

